Apparatus for and methods of die bonding

ABSTRACT

Apparatus for and methods of bonding electrical components or semiconductor chips to a substrate or lead frame is disclosed. According to the present invention, a sawn semiconductor wafer is held upside down in a first substantially horizontal plane and the substrate or lead frame to which it is to be bound is held in a second plane which is below and substantially parallel to the first plane. A die eject head located above the sawn wafer cooperates with a die bond head located between the wafer and the substrate to remove an individual die from the sawn wafer. The die bond head then rotates about an axis which is parallel to both planes and places the die on the lead frame. Also included is a transducer means which is responsive to electrical stimulus for actuating the die eject head and the die bond head such that the interactive force between the heads and the component may be precisely controlled. A die locating system which is located at least in part between the first and second planes, is also provided for producing an image of the candidate die to be transferred. The configuration of the die bond head in combination with the mode of operation of the die bonding apparatus allows efficient operation of the die locating system.

This is a continuation of U.S. Ser. No. 863,590, filed May 15, 1986, nowabandoned, which is a continuation-in-part of copending application U.S.Ser. No. 855,009, filed Apr. 22, 1986, now abandoned, which isincorporated herein by reference.

RELATED APPLICATION

This application is related by subject matter to copending applicationU.S. Ser. No. 855,760, filed Apr. 24, 1986, which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

This invention relates to apparatus for and methods of bonding acomponent to a substrate. More particularly, this invention relates toapparatus for and methods of removing small components, such a dies orother electrical components, from a wafer and bonding the components toa substrate.

In the production of electronic circuitry, particularly circuitrycontaining semiconductor chips or dice, there is a need for extremelyrapid and accurate placement of the chip or die on a substrate. In manyapplications a plurality of chips to be placed on the substrate areremovably held upon a thin film prior to being placed on the substrate.Each chip must be removed or extracted from the thin film and rapidlytransferred to the substrate. In some applications, the chip is onlyplaced on the substrate while in other applications it may be held onthe substrate by an adhesive which may also serve as an electricalconnection, heat sink, or both. The chips may be of various sizes andconfigurations and they must be placed on the substrate at preciselocations to an accuracy of a few thousandths of an inch.

Rapid production of high quality chip/substrate assemblies requires aprecision apparatus which incorporates effective quality controlfeatures. For example, in order to remove the chip from the waferwithout damage, it is required that the chip is precisely aligned to thetool or tools which will remove it. It is also necessary that theinteraction between the removing tool or tools and the chip is not soviolent so as to cause damage to the chip. Effective quality controlalso requires that substandard or defective chips be detected and passedby so that the production or sale of a defective chip/substrate assemblyis avoided. It is also required that the tool or tools which place thechip upon the substrate do not do so with such violence so as to causedamage to the chip or the substrate. This is particularly true whencomplex function chips or very large chips are being bonded to thesubstrate by the application of epoxy or some other adhesive. The priorart has satisfied the above listed needs only partially.

Prior art devices generally place the wafer or other component holdingdevice in substantially the same plane as the substrate. Assembly of thechip to the substrate proceeds in assembly-line fashion wherein a pickup head moves along a relatively long horizontal axis between a pickupstation and a placement station. This arrangement often requires thatthe pick up head be movable over long distances and in severaldirections. For example, see U.S. Pat. No. 3,958,740--Dixon in which thepick up head is movable along a horizontal axis, a vertical axis, and isrotatable about the vertical axis. This arrangement not only requirescomplex and bulky pick up head assemblies, but also limits the capacityof the apparatus by making the distance through which the head assemblytravels a function of the size of the wafer and/or the substrate. Thatis, as the substrate and/or wafer size increase, the distance the headmust travel to pickup the die and place it on the substrate will alsogenerally increase. Thus, the time required to produce each assembly isincreased. This is especially important in light of current trend in theindustry toward larger and larger wafers.

Other prior art applications employ carousel type devices having severalstations located along the path of a rotary member as disclosed in U.S.Pat. No. 3,946,931--Bahnck et al. Devices of this type have thedisadvantage of requiring separate and independent stations for theseveral functions required of a bonding apparatus. That is, a device ofthis type consists of a substrate loading station, a substrate aligningstation, a tack bonding station, a substrate monitoring station, a finalbonding station, a second monitoring station, and a substrate unloadingstation. As a result, devices of this type tend to be large andrelatively slow. In addition, devices of this type also hold the waferand the substrate on substantially the same plane. As a result, thedistance the bond head must travel will generally increase as the sizeof the wafer and/or the substrate increases.

As already mentioned, a device which produces an unnecessarily largeforce on the chip during the transfer process can damage or destroy thechip or the resulting chip/substrate assembly and thereby reduce theeffective capacity of the apparatus. On the other hand, a device whichdoes not utilize sufficient removal or placement force when transferringthe chip from the wafer to the substrate can cause missed pickups orpoorly bonded chips. Thus, the ability to regulate or adjust the pickupand/or placement force according to the dictates of the particularapplication would increase apparatus efficiency and thereby improveproductivity. In addition, the advantage of providing an adjustable toolfor reducing violent chip/substrate interaction may become moreimportant in the future. This is so because Gallium Arsenide (GaAs)chips, which are relatively fragile, are potentially the "chip of thefuture". See for example SMTRENDS, Volume 2, No. 12, page 3, column 3.The prior art, however, has used pickup and placement techniques whichprovide little or no ability to adjust the pickup and placement force.For example, the devices disclosed in U.S. Pat. Nos. 4,166,562--Keizeret al and 4,500,032--Ackerman both utilize spring loaded actuating meansfor unloading and loading the chip. U.S. Pat. No. 3,946,931--Bahnck etal. discloses the use of a mechanical lever arm for removal andplacement of the chip. None of the these devices permit readyadjustment.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide fasterand more efficient methods of assembling components.

It is another object of the invention to substantially reduce the sizeand complexity of the apparatus used for transferring components from awafer to a substrate.

It is a further object of this invention to substantially increase therate of component assembly by minimizing the distance through which thetransfer tool or tools must travel.

It is a further object of this invention to increase the effectiveproduction rate of a component assembly apparatus by minimizing thedamage to the components caused by interaction of the assembly tool withthe component.

It is another object of this invention to increase the productivity of acomponent assembly apparatus by providing an apparatus which does notlimit the size of the wafer or substrate utilized in the assemblyprocess.

Accordingly, a particular apparatus of this invention includes acomponent holding means for holding the component in a first plane, asubstrate holding means for holding the substrate in a second planesubstantially parallel to and spaced from the first plane, and meansmovable between a pickup position and a placement position for transferof the component from the holding means to the substrate such that thecomponent travels through a path which is not primarily parallel to saidplanes.

According to one aspect of this invention, the tool used in a componentassembly apparatus for transfer of the component comprises a means forinteraction with the component, and a transducer means responsive toelectrical stimulus for actuating the interacting means such that theinteractive force between the tool and the component is related to theextent of the electrical stimulus.

According to another aspect of the present invention, a die removingapparatus comprises a component holding means and a substrate holdingmeans for holding the wafer and the substrate in spaced and parallelplanes, an optical means for sensing the position of the die, includingmirror means located between the first and second planes for directinglight towards and away from the die, and a die bond head between thefirst and second planes. The die bond head is rotatable about an axisparallel to the first and second planes and includes a bond head housingand a die engaging tool movably mounted to the housing such thatrotation of the bond head does not interfere with the optical means.

A particular method for the practice of this invention includes holdingthe wafer and substrate used in the assembly process in spaced andsubstantially parallel planes, removing the component from the waferwith a pickup tool located between the planes and adapted to releasablyhold the component, rotating the tool about an axis substantiallyparallel to the planes, and placing the component on the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation view of the die bonding apparatus accordingto one embodiment of this invention.

FIG. 2 is a detailed elevation view of the die bonding apparatus of FIG.1 showing in more detail the die eject head, die bond head, and theoptics used in this invention.

FIG. 3 is a top plan view of the die bond head and the optics associatedtherewith, taken substantially along line 3--3 of FIG. 2.

FIG. 4 is a cross-sectional view of the die eject and die bond headtaken substantially along line 4--4 of FIG. 2.

FIGS. 5a through 5f are sequential views of the die bond and the dieeject heads according to this invention as the die is removed from thewafer and transferred to the substrate.

FIG. 6a is a plan view of the wafer used with this invention.

FIG. 6b is a detailed plan view of the die used with this invention.

FIG. 6c is a detailed plan view of the substrate used with thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The Wafer and the Substrate

The present invention is described in relation to an apparatus forbonding a microchip, also known as a die, to a bond site on a metallizedsubstrate. It will be appreciated by those skilled in the art that thisinvention may be readily used in many applications requiring the removalof a component from a holding means and placement of that component ontoa substrate. In the preferred embodiment of this invention, a thinadhesive film 100A is used to hold a matrix of dice while a metallicsubstrate provides the bond site as shown in FIGS. 6a through 6c. Thewafer, as disclosed in FIG. 6a, comprises a thin adhesive film 100Amounted to a metal or plastic frame 100. A semiconductor wafer 100B isattached to the film 100A and sawn on the film into individual dice 101.FIG. 6c shows the metallized substrate 102 to which the die 101 is to bemounted or placed. The die is to be placed precisely at the bond site102A of the substrate 102. The embodiment described below is directedtowards transfer of the die 101 from wafer 100 to the substrateplacement site 102A of the substrate 102.

The Apparatus in General

The die bonding apparatus, generally referred to as 10, is disclosed inFIG. 1. The die bonding apparatus 10 contains substrate holding tray 11for holding a plurality of substrates 102. The substrate is placed byand one of several mechanisms well known in the art onto a substrateholding means, which in the preferred embodiment is substrate locatingtrack 12. The substrate is moved from holding tray 11, along track 12,and to product tray 13, where it is removed from the track to theproduct tray by any one of several mechanisms well known in the art. Asthe substrate travels from tray 11 to tray 13, it will stop, ifrequired, at epoxy station 14 for the application of adhesive. Thesubstrate 102 then continues along track 12 until a bond site 102A is ata placement location in aligned registry below the die bond head,generally designated as 15. Anyone of several means well known in theart for operating track 12 so as to cause the registry of bond site 102Aat the placement location may be used. In FIG. 1, the die bond head 15is for the most part shown in phantom by the dash lines since it ishidden by optical portion 16.

Sawn wafer 100B is held by a component holding means in a plane spacedfrom and substantially parallel to the substrate holding means. In thepreferred embodiment of this invention, the component holding meanscomprises XY table 17. As the term is used herein, an XY table refers toany means well known in the art for holding a wafer frame in a givenplane while having the capacity to move that wafer to various positionswithin the plane. In the preferred embodiment of this invention, the XYtable holds the wafer in a substantially horizontal plane. In order tomore clearly describe the invention, the following three reference axeswill be referred to: the X axis, the Y axis, and the Z axis. The Z axisis that line which passes through the central axis of die eject head 18and chuck 19 of bond head 15 as shown in FIG. 1. The Y axis is that axiswhich perpendicularly intersects the Z axis where the Z axis intersectssawn wafer 100B thereby creating a substantially vertical ZY plane. TheX axis is that axis which is perpendicular to both the Z and the Y axesand intersects each of those axes at the same point thereby creating asubstantially horizontal XY plane coincidental with wafer sawn 100B. TheXY plane is best revealed in FIG. 3. It will be appreciated by thoseskilled in the art that the designation of the X, Y, and Z axes in thisfashion is completely arbitrary and is used for illustration andreference purposes only. XY Table 17 holds wafer frame 100 so as to besubstantially immobile in the Z direction while having means to movewafer frame 100 within the XY plane. In this way, each die 101 may beplaced in a pickup location in aligned registry directly above center ofrotation of the die bond head 15 and directly below die eject head 18.Anyone of several means well known in the art for moving XY table withinthe XY plane may be used. The means and apparatus used in conjunctionwith the XY table to precisely place die 101 in the pickup location isdescribed later in the specification and in copending application U.S.Ser. No. 855,760, filed Apr. 24, 1986, assigned to the assignee of thisinvention. With both die 101 and bond site 102A in proper registry, dieeject head 18 and die bond head 15 combine to remove the die from thewafer, whereupon the die bond head rotates to move die 101 into alignedregistry with the bond site, as best shown in FIG. 4. The die bond head15 then places the die 101 in the proper bond site 102A and returns tothe position shown in FIG. 1. When all the bond sites on each substratehave a die bonded thereto or placed thereupon, the substrate continuesalong track 12 and is loaded into substrate product tray 13.

Die Removal and Placement--Apparatus

Referring now to FIG. 1 and 2, an important feature of this inventionresides in the spatial relationship between sawn wafer 100B andsubstrate 102. According to this invention, die bonding apparatus 10 isconfigured so as to hold dice 101 in a first plane which is spaced fromand substantially parallel to a second plane in which the substrate isheld. In the preferred embodiment, wafer frame 100 is held in an"upside" down fashion by XY table 17 in the substantially horizontal XYplane. The "upside" or sawn wafer side of wafer frame 100 faces downwardtoward substrate 102, as is shown in FIG. 2. In this embodiment,substrate 102 is held in a substantially horizontal plane below waferframe 100. By maintaining the spatial relationship disclosed herein, theXY dimensions of sawn wafer 100B and substrate 102 are theoreticallylimitless since the planes will never intersect. In this way, theoverall bonding time per die is reduced since the time required per dieto load and unload the wafer and/or substrate decreases as the size ofthe wafer and/or substrate increases. In addition, by locating thesubstrate and wafer in spaced and parallel planes, the distance and timerequired to transfer die 101 from wafer 100B to bond site 102A isminimized. This is so because the distance between the die and thesubstrate is not a function of the wafer or substrate size. Therefore,in the preferred embodiment of this invention, the substrate bond site102A is placed directly below the die to be removed. In this way, thedistance through which the die must travel from the wafer to thesubstrate may theoretically be reduced to the distance between theplanes. This is especially significant in light of the rapid advancementin the production of small or miniature precision tools. As precisiontooling allows bond die head 15 to be made with smaller and smallerdimensions, the distance between the wafer and the substrate canaccordingly be reduced. The reduced distance between the substrate andthe wafer will in turn result in a shorter time required for the chip tosubstrate transfer. The spacial relationship between wafer frame 100 andsubstrate 102 as disclosed by this invention is also extremelysignificant for embodiments in which no tools are placed between theplanes. That is, the tool or tools used to transfer die 101 to substrate102 may be contained entirely above wafer 100 and/or below substrate102. In embodiments of this type, the distance the die 101 must travelfrom wafer 100 to bond site 102A can be reduced to negligibledimensions. Accordingly, it will be appreciated by those skilled in theart that the spacial relationship between sawn wafer 100B and substrate102 disclosed in this invention permits significant advances in the rateat which chip/substrate assemblies are produced.

The apparatus used for transferring a die 101 from sawn wafer 100B to abond site 102A on substrate 102 will now be described. It will beappreciated by those skilled in the art that while this invention isdescribed with regard to the removal of a small semi-conductor chip,also known as a die, from a thin adhesive film to a bond site on ametallized substrate, the apparatus made according to this invention maybe easily adapted to remove components other than dies from supportingstructures other than adhesive film and place those components on asupporting structure other than a metallized substrate.

Referring now to FIGS. 2, 3 and 4, the component transfer means fortransferring die 101 to substrate bond site 102A is disclosed. FIG. 2reveals a close-up view of the central portion of the component transfermeans of this invention. In this view, the light source used inconjunction with optics 16 of this invention has been substantially cutaway to more fully reveal die bond head 15. Die bond head 15 is locateddirectly below die eject head 18. Die 101 is in a pickup locationbetween the die bond head 15 and die eject head 20 and is ready forremoval from the wafer. Die 101 is precisely placed in this position byXY table 17 by any one of several means known in the art or in themanner described in detail later in the specification. As best revealedin FIG. 4, the component transfer means of this invention comprises atool, generally designated as 19, movably mounted to the housing portion50 of head 15, which in turn is rotatably mounted to frame 20 of diebonding apparatus 10. The die bond head 15 is rotatable about the axislabeled 21 in FIG. 4. Axis 21 is parallel to and aligned with the X axisas shown. The central shaft 23 of the die bond head 15 is supported bybearings 24 in frame 20 and is rotatably attached to motor 22 forrotation about axis 21. Tool 19 is movably mounted to bond head 15 suchthat the movement of tool 19 is normal, or perpendicular, to the diewhen in the position shown in FIG. 4. More particularly, tool 19 ismovably mounted to housing 50 such that movement of tool 19 isperpendicular to axis 21. Shafts 25A and 25B which are attached to tool19 on one side, pass through a pair of channels 26A and 26B in bond head15 and are connected on the other side thereof to connecting plate 27.Connecting plate 27 is in turn attached to an actuating means mounted tothe die bond heat 15. This actuating means may be anyone of severalactuating means well known in the art, or preferably the actuating meanswhich is shown in FIG. 4 and described latter in the specification. Thetool 19 can be actuated towards and away from die 101 when in theposition indicated by the solid lines in FIG. 4, and towards and awayfrom substrate 102 when in the position indicated by the dashed lines inFIG. 4. In the preferred embodiment of this invention, tool 19 isplastic part comprised of a V shape base portion 19B, an arm 19C, and anend portion 19D. As best revealed in FIGS. 3 and 4, the arm 19C extendsfrom the base portion 19B and supports end portion 19D. The face 19A isthat portion of tool 19 which actually engages die 101 during thetransfer process.

A vacuum, generated by any means well known in the art, may be appliedto vacuum port 28 in die head 15. The vacuum passes through channel 28Aand is then passed to vacuum port 29 in chuck 19 by vacuum hose 30.Channel 31 in tool 19 passes from vacuum port 29 to the face 19A (seenin FIG. 3) of tool 19. Application of vacuum to port 28 thus providestool 19 with an interacting means or, more particularly, a grippingmeans on the end thereof. In this way, die 101 may be releasably held bythe vacuum when the face 19A of chuck 19 is placed in contact with die101 and vacuum is applied to vacuum port 28.

Referring once again to FIG. 2, die eject housing 32 is movably mountedto frame 20 of die bonding apparatus 10. Housing motor 33 is mounted tohousing 32 in any conventional manner so as to actuate the housingtowards and away from wafer frame 100B. In this way, die eject head 18,which depends from housing 32, can move to a noninterfering positionwith respect to wafer frame 100 so that spent wafer frames can beremoved from and new frames placed upon XY table 17. Referring onceagain to FIG. 4, the central portion of the die eject assembly isrevealed in cross-section. Die eject head 18 is adapted to releasablyhold the film side of wafer frame 100 by means of a vacuum. A vacuum,generated by any conventional means well known in the art, istransmitted to the end of die eject head 18 by vacuum channels 36A and36B. Seal ring 43 is coupled to the end of die eject head 18 so that theend of the die eject head will normally sealably engage the film side ofwafer frame 100, and thereby releasably hold the wafer against thesurface of the die eject head. When vacuum is applied to die eject head18, the flexible sawn wafer 100B conforms to the slight concave surfaceof the head. The concave surface of die eject head 18 deforms wafer 100Band achieves the following two objectives: (1) it facilitates removal ofdie 101 by "pre-deforming" the wafer, and (2) it enhances recognition ofthe die to be removed, as disclosed in copending application U.S. Ser.No. 855,760, filed Apr. 24, 1986.

The configuration and use of the two vacuum channels 36A and 36Bprovides an important feature of this invention. In the preferredembodiment of the invention, each channel is connected to anindependently operated vacuum generating means. As best disclosed inFIG. 4, channel 36A applies vacuum primarily to the outer portion of dieeject head 18, while channel 36B applies vacuum primarily to the centralportion of the die eject head. By connecting each channel toindependently controlled generating means, the extent of "grip" on film100A can be adjusted along the radial direction of die eject head 18.Thus film 100A may be gripped tightly at the periphery of die eject headand relatively loosely at the center in order to facilitate removal ofthe die 101. In another embodiment of this invention, one or both ofchannels 36A and 36B may be alternatively attached to a positivepressure generating means, such as a small pump for example. In thisway, an air bearing may be created between the film 100A and the end ofdie eject head 18 so that the die 101 to be removed is more efficientlyplaced at the proper pickup location, as discussed in more detail laterin the specification.

Die eject head 18 depends from housing 32 and is mounted thereto bymounting bolt 40. Actuating means, generally designated as 41, isaligned with die eject head 18 and is mounted to housing 32. Thisactuating a means may be anyone of several actuating means well know inthe art, or preferably the actuating means shown in FIG. 4 and describedin detail latter in the specification. Connecting shaft 35 is containedwithin multi diameter chamber 35A of actuating means 41 and multidiameter chamber 35B of die eject head 18. Connected to the lowerportion of connecting shaft 35 is die eject pin 38. Also attached to thelower end of connecting shaft 35 is resilient spring 39 which connectsthe end of shaft 35 to the bottom of channel 35B and thereby normallyurges shaft 35 in an upward direction. The upper end of shaft 35 isattached to actuating means 41. In this way, die eject pin 38 isactuatable to a protruding position with respect to the lower end of dieeject head 18, thereby deforming the film 100A on the backside of wafer100B and aiding in the removal of die 101 from the wafer. The detailsconcerning the exact removal and placement process utilized with theapparatus of this invention is disclosed in detail below.

Die Removal and Placement--Method

When the apparatus of this invention as previously described is usedaccording to the methods of this invention, an advantageous die bondingsystem is achieved. Accordingly, FIGS. 5a through 5f disclose sequentialviews of the apparatus of this invention being used according to oneembodiment of this invention. Referring to FIG. 5a, a magnified view oftool 19 and die eject head 18 in a preremoval position is disclosed bythe solid lines. Die 101 has been moved to a pick-up location inalignment with die eject head 18 and tool 19 by the XY table. Themethods and apparatus used for precisely locating die 101 in thisposition is disclosed later in the specification. When die 101 isproperly located as disclosed in FIG. 5a, vacuum is applied by anyconventional vacuum generating means to chambers 36A and 36B asdisclosed by the arrows marked vacuum in that Figure. This vacuum, inconjunction with seal ring 43, serves to releasably hold the film 100Aagainst the slightly concave lower surface of die eject head 18. Dieeject pin 38 provides an interacting means for deforming wafer film 100Aand thereby aiding in the removal of die 101 from the wafer. In theposition shown in FIG. 5a, the axis of die eject pin 38 is aligned withthe center of die 101. A vacuum is also applied by any conventionalvacuum generating means to the face 19A of tool 19 through chamber 31.Face 19A thereby provides a second interacting means for removablyholding die 101. In this position, the central axis of the face 19A oftool 19 is also aligned with the center of die 101. Therefore, thecentral axis of the face 19A of tool 19, the axis of die eject pin 38,and the center of die 101 are all coincidental with the Z axis as shownin FIG. 5a. Once in the position disclosed by the solid lines in FIG.5a, tool 19 is actuated towards die eject head 18 until the surface 19Aof tool 19 contacts die 101 as shown by the dashed lines in FIG. 5a. Inthe preferred embodiment of this invention, the force with which toolface 19A contacts die 101 is adjustable by adjusting the electricalstimulus to the actuating means as disclosed later in the specification.In the preferred embodiment of this invention, movement of tool 19 fromthe position disclosed by the solid lines in FIG. 5a to the positiondisclosed by the dotted lines in FIG. 5a is carried out in a time lessthan about 50 milliseconds.

Once the face 19A of tool 19 has contacted die 101, the die is removedfrom wafer 100B as disclosed in FIG. 5b. In this Figure, die eject pin38 has been actuated into a protruding position relative to the end ofdie eject head 18 so as to deform film 100A in the immediate vicinity ofdie 101. In the preferred embodiment, the independent application ofvacuum as provided by channels 36A and 36B is advantageously employedduring this step. That is, the vacuum applied to the central portion ofdie eject head 18 is relatively weak in order to facilitate deformationof film 100A, while the vacuum applied to the peripheral portion of thedie eject head is relatively strong so that the film remains stable. Insynchronized fashion, tool 19 has been actuated away from wafer 100B asdie eject pin 38 is actuated to the protruding position seen in FIG. 5b.It should be noted that the vacuum applied to die eject head 18 and tool19 continues to exist through this step. The vacuum applied to die ejecthead 18 insures that the deformation of wafer film 100A occurssubstantially only in the region of die 101 to be ejected. The vacuumapplied to tool 19 insures that as the adhesive bond between die 101 andfilm 100A is broken, the die is held firmly and precisely on the face19A of the tool. In the preferred embodiment, the force used foractuating die eject pin 38 and tool 19 may be adjusted by the adjustableactuating means discussed later in the specification. In this way, onlythat force required to remove die 101 from film 100A is applied andtherefore the risk of damage to the die is minimized. In the preferredembodiment of this invention, the die moves from the position shown bythe dotted lines in FIG. 5a to the position shown in FIG. 5b in lessthan about 50 milliseconds.

Once die eject pin 38 has been actuated out of die eject head 18 apredetermined distance as shown in FIG. 5b, the pin is retracted to anonprotruding position as disclosed in FIG. 5c. While pin 38 isretracting into die eject head 18, tool 19 continues to be actuated awayfrom wafer frame 100 so as to insure that die 101 is fully removed fromthe wafer and in a noninterfering position with the dice that remain onthe wafer. In a preferred embodiment of this invention, movement ofapparatus from the position disclosed in FIG. 5b to the positiondisclosed in FIG. 5c requires less than about 30 milliseconds. Once theposition as disclosed in FIG. 5c is achieved, XY table 17 will begin tomove wafer frame 100 so as to locate the next die to be removed in theproper pick-up location. In one embodiment of this invention, channel36A or channel 36B may be adapted to receive application of positivepressure thereto so that the movement of the wafer frame 100 will befacilitated during this step. For example, channel 36A may be connectedto a vacuum generating means while 36B is connected to a means forgenerating positive pressure. During the steps disclosed in FIGS. 5a and5b, vacuum is applied to channel 36A so as to grip film 100A so that die101 may be removed. Once die 101 is removed as disclosed in FIG. 5c, thevacuum generating means is disconnected and a positive pressure isapplied to channel 36B. This positive pressure will create a cushion ofair or an "air bearing" between film 100A and the end of die eject head18. In this way, film 100A travels on a relatively friction free cushionof air so that the film moves easily under die eject head 18. Thisresults in the ability to more precisely place the next die at theproper pickup location since friction between the film and the end ofthe die eject head does not interfere with the smooth operation of XYtable 17.

Once the position disclosed in FIG. 5c has been achieved, tool 19 isrotated substantially 180° about axis 21 (as shown in FIG. 4). Thisrotation results in the alignment of face 19A of tool 19 with bond site102A as shown in FIG. 5d. It should be noted that bond site 102A isplaced in a placement location by means which are conventional in theart and form no part of this invention. In the preferred embodiment ofthis invention, the placement location is such that the center of bondsite 102A is coincidental with axis Z. In this way, rotation ofsubstantially 180° by tool 19 brings die 101 into precise registry abovebond site 102A. As disclosed in FIG. 5d, bond site 102A has received anapplication of epoxy or adhesive prior to being moved to the placementlocation. In the preferred embodiment, movement of the apparatus fromthe position indicated in FIG. 5c to the position indicated in FIG. 5dis accomplished in less than about 60 milliseconds.

Once in an aligned and registered position as disclosed in FIG. 5d, tool19 is actuated towards substrate 102 so as to place die 101 precisely onbond site 102A as disclosed by the dash lines. In the preferredembodiment of this invention, the force exerted upon die 101 andsubstrate 102 as tool 19 places the die upon the substrate is adjustableaccording to adjustment of the preferred actuating means disclosed laterin the specification so that the risk of a defective chip/substrateassembly is minimized and suitable attachment to the epoxy or adhesiveis made. Movement of the apparatus from the position disclosed in FIG.5d to the position disclosed in FIG. 5e is achieved in less than about30 milliseconds in the preferred embodiment. Once the position disclosedby the dash lines in FIG. 5e is achieved, the vacuum applied to chamber31 of tool 19 is removed and face 19A of tool 19 no longer engages die101. With the vacuum removed, tool 19 is actuated away from substrate102 to the position indicated by the solid lines in FIG. 5e so as torelease die 101. With die 101 properly placed on substrate 102, thesubstrate resumes its movement along track 12 so as to bring the nextbond site 102A to a placement location coincidental with axis Z.

Once tool 19 has reached the position as shown by the solid lines inFIG. 5e, the tool is normally rotated about axis 21 (see FIG. 4) 180°and returns to the position disclosed in FIG. 5a. It should be notedthat in the preferred embodiment tool 19 subtends substantially the samearc in its return to the position of FIG. 5a as was subtended by thechuck in moving from the position disclosed in FIG. 5c to the positiondisclosed in FIG. 5d, as long as the valid die 101 can be discerned andpresented by the XY table. By oscillating back and forth in this manner,the optics 16 are locatable substantially to the right of the XZ planeas disclosed in FIGS. 3 and 5f. Referring now to FIG. 5f, chuck 19 isseen in a pause position after having rotated substantially only 150°.While this step is not normally included, it is used in the event that asuitable die 101 has not been properly located in a pickup locationprior to the return of tool 19 to the position disclosed in FIG. 5a.This pausing step allows the optics 16 of this invention to continue tofunction until the die 101 has been properly located. As revealed inFIG. 5a, if tool 19 were to rotate a full 180° the functioning of optics16, which includes mirror 45, would be obstructed and die 101 could notbe properly located. On the other hand, it will be appreciated by thoseskilled in the art that the pausing step as disclosed in FIG. 5f is notrequired if the die 101 has been properly located prior to the time tool19 reaches the pause position.

Die Bond and Die Eject--Actuation

Referring now to FIG. 4, the preferred apparatus for causing actuationof die eject head 18 and die bond head 15 is disclosed. In the preferredembodiment of this invention, die eject head 18 and die bond head 15 areeach actuated by a separate moving coil transducer as shown in FIG. 4.Referring first to die bond head 15, housing 50 is mounted to mountingflange 51 which is in turn mounted to a central shaft 23 for rotationthereby. Housing 50 has a chamber therein which substantially enclosesthe cylindrical magnet 52 and voice coil 53 of the transducer. Aspreviously described, support plate 27 is attached to the lower portionof voice coil 53. Support plate 27 in turn supports and has mountedthereto left and right linear bearing shafts 25A and 25B. Voice coil 53is in electrically conductive contact with an electrical energy sourceand receives electrical stimulus thereby. The electrical energy sourceand the means for connecting the energy source to the voice coil can beachieved by any one of several methods well known in the art and istherefore is not shown in FIG. 4. According to principles well known inthe art, electrical stimulation of voice coil 53 causes an interactionbetween the coil and the transverse magnetic field disposed thereabout,said interaction causing the actuation of voice coil 53 with respect tomagnet 52. Magnet 52 is securely mounted to housing 50 and thereforeelectrical stimulus of coil 53 causes the movement of plate 27 withrespect to housing 50. In the preferred embodiment of this invention,the general features of the moving coil transducer assembly describedabove are well known in the art and moving coils of this type may bepurchased from any of several well known manufacturers. The exact movingcoil to be used is a function of many parameters of the die bondingapparatus in general, including size, speed, and cost. In the preferredembodiment of this invention, the die bond moving coil is available fromSystems Magnetics Corporation of Anaheim, Calif. or Kimco Corp. ofCalif. Other embodiments of this invention may include replacing themoving coil described above with a moving iron transducer, anelectrostatic transducer, a magnostrictive transducer, or apiezoelectric transducer. As is well known in the art, each of theactuating means described above is characterized in that the force andextent of actuation is functionally related to the extent of electricalstimulus applied. This feature embodies an important aspect of thisinvention in that adjustment of the electrical stimulus supplied to thetransducer effects adjustment of the force and rate with which tool 19is actuated. In this way, the force with which tool 19 engages andremoves die 101 from wafer 100B and the force with which tool 19 placesor bonds die 101 to substrate 102 is adjustable according to theelectrical stimulus applied to the transducer.

Die bond head 15 of this invention also includes a tool locating meanscentrally disposed within housing 50 for locating tool 19 relative towafer frame 100 and substrate 102. Core 54 is attached to support plate27 and is centrally disposed within housing 50. When coil 53 is actuatedby an electrical stimulus as described above, core 54 moves relative tocylindrical coil 55. Thus, the interaction of core 54 with coils 55comprises a reluctive displacement transducer which acts according toprinciples well known in the art for sensing the position of tool 19. Inthe preferred embodiment of this invention, the reluctive displacementtransducer is a linear-variable differential transformer (LVDT). ThisLVDT may be any one of several appropriate off the shelf LVDT's havingtransduction characteristics well known in the art. In a preferredembodiment of this invention, the LVDT used with bond head 15 of thisinvention is a 222C-K019 LVDT manufactured by Robinson-Halpern. Inanother embodiment, an inductance bridge may be used as a locatingmeans.

Directing attention to actuating means 41, the means for actuating pin38 of die eject head 18 is described. The die eject head actuating means41 comprises a cylindrical housing 56 mounted to housing 32. Cylindricalmagnets 57 are contained within and mounted to housing 56. A voice coil42 is contained within the magnetic field created by the magnet and ismounted to support shaft 35 by bolt 58. Magnets 57 and voice coil 42thus comprise a moving-coil transducer which acts according toprinciples well known in the art. As described earlier, application ofelectrical stimulus to voice coil 42 by any means well known in the artproduces an interaction between the voice coil and the magnet such thatsupport arm 35 and hence die eject pin 38 are actuated thereby. Themoving coil of this invention is any appropriate well known moving coilmanufactured by anyone of several well known manufactures. The exactmoving coil which will be used is a function of many parameters of thedie bonding apparatus in general, including size, speed, and ultimatecost. In the preferred embodiment of this invention, the die ejectmoving coil is available from Systems Magnetics Corporation of Anaheim,Calif. or Kimco Corp. of California. Other embodiments of this inventionmay include replacing the moving coil described above with a moving irontransducer, an electrostatic transducer, a magnostrictive transducer, ora piezoelectric transducer. As is well known in the art, each of theactuating means described above is characterized in that the force andextent of actuation is functionally related to the extent of electricalstimulation applied. This feature embodies an important aspect of thisinvention in that adjustment of the electrical stimulus applied to thetransducer effects adjustment of the force and rate with which die ejectpin 38 is actuated. In this way, the force with which die eject pin 38deforms film 100A and thereby interacts with die 101 is adjustableaccording to the electrical stimulus applied to the transducer.

The position of die eject pin 38 relative to wafer 100B is sensed in thepreferred embodiment of this invention by core 59. Core 59 is mounted tovoice coil 42 and travels within cylindrical coil 60. Core 59 and coil60 thus comprise a reluctive displacement transducer which, in thepreferred embodiment of this invention is an LVDT. Thus, according toprinciples well known in the art, movement of die eject pin 38 relativeto wafer 100B is detectable and sensible by the LVDT disclosed herein.Once again, the LVDT used with die eject head 18 is anyone of severalLVDTs well known in the art which are available from anyone of severalmanufacturers. In the preferred embodiment of this invention, the LVDTused with the die eject head is a 2226-K019 LVDT manufactured byRobinson-Halpern. In another embodiment, an inductance bridge may beused as a locating means.

The actuating means disclosed in this section of the specificationprovide the important adjustability feature of this invention. Thisadjustability feature is enhanced when combined with the locating meansprovided by the LVDTs described above. That is, the LVDT's supplyinformation concerning the position and rate of movement of tool 19 ordie eject pin 38. With this information thus sensed, a basis forregulating the extent of electrical stimulus to the actuating means ofthis invention is provided. This combination has the distinct advantageof being adjustable according to the particular instantaneous operationof the apparatus. In particular, this combination is well suited for usewith a computer wherein the signals generated by the LVDT are input andsignals for regulating the extent of electrical stimulus are output.

Die Locating Means

Referring now to FIG. 1, the optics of this invention, generallydesignated as 16, are revealed. Optics 16 are used in conjunction withXY table 17 to precisely locate the die 101 in a proper pickup location.Portion 16A of optics 16 contains a light source and various mirrors andlenses used to conduct light along the precise path indicated by thearrows marked L in FIG. 3. Portion 16B of optics 16 contains an opticalreceptor or camera for receiving optical input from portion 16A.

Referring now to FIG. 3, optics 16 and die eject head 15 are seen in aplan view from above die bond head 15. Light source 60 provides lightwhich passes through lens 61 and 62. Light is then directed towardsmirror 63 by slotted mirror 64. Slotted mirror 64 insures that themajority of the light from source 60 is directed towards mirror 63.Mirror 63 sits on a substantially 45° angle with respect to a horizontalplane and thus directs the light rays substantially perpendicular towafer frame 100. It should be noted that a die 101 is placed in a properpick-up location with the aid of optics 16 during that period of time inwhich tool 19 has been rotated out of an interfering position withrespect to the path of light. That is, optics 16 operates to locate die101 in a pickup position starting immediately after tool 19 moves fromthe position indicated in FIG. 5c. Tool 19 will not return to theposition shown in FIG. 5a until a new die has been located at the pickuplocation. Thus, while die bond head 15 is performing the task of bondinga die to substrate 102, light source 60 provides means by which camera65 can sense the position of a die 101 in the vicinity of the properpickup location. The optics of this invention thus not only provide themeans for locating die 101 but also a means for indicating the presenceof a defective or substandard die in the pickup location. Additionaldetails concerning the operation and function of optics 16 are disclosedin copending application U.S. Ser. No. 855,760, which has beenincorporated herein by reference.

An important feature of this invention resides in the particularconfiguration of bond head 15. Referring to FIGS. 2 and 3, it is clearthat the optics portion of this invention requires a clear field of viewin order to properly create an image of a die 101. Accordingly, housing50 of bond head 15 does not interfere with the optics of this invention,as best revealed in FIG. 3. In particular, the most forward portion,i.e., the portion closest to mirror 63, of housing 50 is front face 50A.As the terms are used herein, forward and behind refer to relativepositions in the x direction with respect to mirror 63. The front face50A of the housing is held in a position directly behind mirror 63 so asnot to interfere with any light reflected by that mirror toward die 101.The major portion of housing 50 and therefore bond head 15 is never in aposition of interference with the light which illuminates die 101 and isreflected back to camera 65. That is, since housing 50 is only requiredto rotate 180° about axis 21 during the transfer operation, the housingnever moves into interference with the optics. Accordingly, only arm 19Cand end 19D of tool 19 are ever in an interfering position with respectto the path of light required by the optics, as indicated by the arrowsmarked L in FIG. 3. However, due to the dog-leg configuration of tool19, as best revealed in FIG. 4, only a slight rotation of the housing 50will move the tool 19 into a non-interfering position. The uniqueconfiguration of tool 19 also allows face 19A to be positioned directlybelow die 101 without interfering with the mirror 63 and 64. Overall,therefore, the dog-leg shape of tool 19 in combination with the opticalconfiguration and mode of operation of the die bonding apparatus impartsthe following benefits: first, since only the "natural" transferringmotion of housing 50 is required to move the tool out of the path oflight, the cost and imprecision of a second degree of freedom ofmovement for the housing is avoided; and second, since arm 19C "swingsaround" mirror 64 during the "natural" transferring motion of thehousing, the optics portion of this invention is maintained in a simple,inexpensive configuration.

Another advantage of tool 19 and the manner in which it is mounted tohousing 50 is that it provides a safety feature for the die bondingapparatus in the event that control of the tool is lost In normaloperation, the actuating means of die bond head 15 holds tool 19 in aprecisely controlled position during each phase of the transfer processso as to avoid unwanted interference with the components to beassembled. In the event control of tool 19 is lost, due to failure ofthe actuator for example, it is desirable to insure that tool 19 willnot damage either substrate 102 or wafer 100B as head 15 continues torotate at high speed. Accordingly, the assembly comprising tool 19,shafts 25A and 25B, connecting plate 27, and voice coil 53, isconfigured such that the center of gravity of the assembly is alwaysbelow axis 21 relative to tool 19. Tool 19 is therefore a low mass buthigh strength plastic tool configured as shown in the attached figures.In this way, tool 19 is held in the retracted position by centrifugalforce during rotation of bond head 15 when the actuating means isrendered inoperative.

Although particular embodiments of this invention have been described indetail for purposes of illustration, it will be appreciated that variousmodifications are within the spirit and scope of this invention. Theappended claims are intended to cover all such modifications.

What is claimed is:
 1. An apparatus for removing a die from a filmmounted wafer containing a plurality of dice and bonding the die to abond site on a substrate having a plurality of bond sites thereon, saidapparatus comprising:(a) component holding means for holding the waferin a first plane and moving the wafer within said first plane so as toplace the die at a pickup location; (b) substrate holding means forholding the substrate in a second plane spaced from and parallel to saidfirst plane and moving the substrate so as to place the bond site at abond location; (c) optical means for sensing the position of said die,including mirror means located between said first and second planes fordirecting light towards and away from said die; and (d) a die bond headbetween said first and second planes rotatable about an axis parallel tosaid first and second planes, including a bond head housing and a dieengaging tool movably mounted to said housing such that rotation of saidhousing does not interfere with said optical means.
 2. The apparatus ofclaim 1 wherein said die engaging tool is mounted to said housing formovement in a direction perpendicular to said axis of rotation.
 3. Theapparatus of claim 2 wherein:(a) said component holding means includesmeans for holding said wafer upside down in a first substantiallyhorizontal plane; (b) said substrate holding means includes means forholding said substrate below said wafer; and (c) said mirror meansincludes a mirror aligned directly below said pickup location.
 4. Theapparatus of claim 3 wherein the surface of said mirror is at asubstantially 45° angle with respect to said first plane.
 5. Theapparatus of claim 4 wherein said axis of rotation is substantiallyaligned with longitudinal center of said mirror.
 6. The die bondingapparatus of claim 4 wherein:(a) the most forward facing portion of saidhousing is located directly behind said mirror; and (b) said dieengaging tool comprises a base portion held behind said mirror and anarm attached at one end to said base portion and extending out past saidmost forward facing portion of said housing.
 7. The die bondingapparatus of claim 6 wherein said arm extends away from said axis ofrotation.
 8. The device of claim 7 wherein said housing has no freedomof movement other than said rotation.
 9. The device of claim 6 whereinsaid die engaging tool further comprises and end portion attached to theother end of said arm, said end including a face for interacting withsaid die.
 10. The device of claim 9 wherein said end portion has achamber extending therethrough from a first end in said face to a secondend such that a vacuum applied to said second end produces a vacuum atsaid first end.
 11. An apparatus for removing a die from a film mountedwafer containing a plurality of dice and bonding the die to a bond siteon a substrate having a plurality of bond sites thereon, said apparatuscomprising:(a) component holding means for holding the wafer in a firstplane and moving the wafer within said first plane so as to place thedie at a pickup location; (b) substrate holding means for holding thesubstrate in a second plane spaced from and parallel to said first planeand moving the substrate so as to place the bond site at a bondlocation; (c) optical means for sensing the position of said die anddefining an optical path, a portion of said path leading to and awayfrom said die; and (d) a die bond head between said first and secondplanes rotatable about an axis parallel to said planes for movementbetween a pickup position and a placement position, including a majorportion held outside of said optical path and a minor portion which isin said optical path when said bond head is in said pickup position andwhich moves out of said optical path when said bond head rotates fromsaid pickup position towards said placement position.
 12. The apparatusof claim 11 wherein said major portion includes a housing and said minorportion includes a die engaging tool movably mounted to said housing formovement in a direction perpendicular to said axis of rotation.
 13. Theapparatus of claim 11 wherein said optical means includes mirror meanslocated between said first and second planes for directing light towardsand away from said die.
 14. The apparatus of claim 13 wherein saidmirror means includes a mirror aligned directly below said pickuplocation.
 15. The die bonding apparatus of claim 12 wherein said dieengaging tool comprises a base portion held out of said optical path andan arm attached at one end to said base portion and extending into saidoptical path when said bond head is in said pickup position.
 16. The diebonding apparatus of claim 15 wherein said arm extends away from saidaxis of rotation.
 17. The device of claim 16 wherein said housing has nofreedom of movement other than said rotation.